1. Field of the Invention
The present invention relates to a coupler for opening/closing a flow passage by connecting or separating a socket and a plug. In particular, the present invention relates to a coupler provided with an indicating function for indicating the attachment of a plug to a socket.
2. Description of the Related Art
A coupler has been hitherto adopted in order to automatically open/close a flow passage when a plug is connected to a socket or when the plug is separated from the socket. A valve plug is automatically opened/closed by the coupler. Therefore, the flow passage is closed when the plug is separated from the socket. Accordingly, the fluid is prevented from leaking.
In a conventional coupler, an operator observes the coupler to confirm whether or not the plug is reliably attached to the socket. However, when the attachment is checked by visual observation only, it is extremely difficult to find out whether the attachment of the plug to the socket is incomplete. As a result, if the plug is incompletely attached to the socket, the fluid does not flow from the pipe connected with the socket to the pipe connected with the plug.
Alternatively, an operator may directly touch the socket and the plug of each coupler to confirm the attachment. However, when a plurality of couplers are provided, the confirmation by directly touching the couplers is complicated. The maintenance operation is also complicated.